The most separate runs one team has achieved in the Wild Card era is three, a feat accomplished by four teams: the Cubs (2003-2004, 2007-2008, 2015-present), Dodgers (1994-1997, 2004-2009, 2013-present), Mets (1997-2000, 2006-2008, 2015-2016) and Rangers (1996-1999, 2009-2013, 2015-2016). It’s worth remembering that having more windows is not necessarily better — notice how many of these are short, and that only the Cubs won a championship.
Of the 47 playoff windows, seven are ongoing (BOS, CHC, CLE, HOU, LAD, NYY, WAS).
The other 40 can be divided into two categories: normal playoff runs and the monster decade-plus dynasties formed by the 1990s Braves, the curse-breaking Red Sox, the Joe Torre Yankees, and the Albert Pujols Cardinals. Those four teams distort the overall average so much that we will consider them separately.
The 36 traditional playoff windows were open for an average of 4.69 years each. Add the mega-dynasties back in, and that average swells to 5.95 years. So, basically, the typical playoff window is about five years long.
Source: Brian Reihnart, The Hardball Times